The present invention generally relates to an optical interface apparatus and, in particular, relates to such an apparatus wherein a light signal is modulated and/or demodulated by means including a liquid crystal material.
The use of optical fibers in a communication system is advantageous since a substantial amount of information can be conveyed over a relatively physically small optical fiber. In addition, the information is conveyed by optical fibers that exhibit negligible electromagnetic interference or radio frequency interference to the surrounding environment. Further, optical fibers are quite insensitive to such interference emitted from surrounding devices and systems.
Although these advantages have been contemplated and generally known for some time the practical application of optical fiber technology has advanced at a relatively slow pace. One particular impediment is that previously proposed liquid crystal optical switching devices are expensive and difficult to manufacture. For example, light beams associated therewith are required to be very precisely aligned and stabilized to impinge upon a liquid crystal material at the critical angle thereof. Such liquid crystal devices are both expensive to manufacture and are not amenable to mass production techniques.
One reason such devices are expensive to manufacture is that the optical fibers are usually surface mounted thereby requiring all surfaces of the optical fiber device to be ground, lapped and polished to a high degree of optical flatness, for example, to a point-to-point variation of about 20 Angstrom, as well as requiring various adjacent surfaces to be manufactured to the critical angle, all with very small tolerances allowed. Generally, liquid crystal optical devices proposed to date have utilized a pair of trapezoidal prisms having opposing bases with the liquid crystal material disposed therebetween. Hence, not only do the trapezoidal prisms require optical precision in the manufacturing thereof, but the alignment of the two prisms also becomes a precision assembly.
A further drawback of the proposed liquid crystal optical devices is that the crosstalk between the output ports thereof is excessive and the switching time is relatively slow due to the mass and volume of the liquid crystal material utilized. Typical of such proposed liquid crystal switching devices are those described and discussed in U.S. Pat. No. 4,201,442 issued to McMahon et al. on May 6, 1980, U.S. Pat. No. 4,278,327 issued to McMahon et al. on July 14, 1981 and U.S. Pat. No. 4,385,799 issued to Soref on May 31, 1983.
Many of the difficulties associated with the above-described devices have been overcome by devices and techniques such as those discussed and described in U.S. patent application Ser. Nos. 795,156, 795,151, 795,150 and 795,155 entitled LIQUID CRYSTAL OPTICAL SWITCHING DEVICE, LIQUID CRYSTAL OPTICAL SWITCHING DEVICE HAVING A MINIMIZED INTERNAL LIGHT PATH, LIQUID CRYSTAL CELL FOR USE IN AN OPTICAL SWITCH and LIQUID CRYSTAL OPTICAL SWITCHING DEVICE HAVING REDUCED CROSSTALK respectively, all filed on even date herewith and assigned to the assignee hereof. These applications are deemed incorporated herein by reference.
In consideration of the above, an optical interface apparatus particularly adapted to modulate and/or demodulate a light signal directly from/to a digital, or pulsed, signal is highly desirable to fully realize the advantages of optical fiber technology.